Generally, a conventional lens has a single focal length to provide a particular visual acuity. The lens may be produced for a particular lens wearer or application where there is no change in visual acuity or no need to modify the visual acuity for different viewing distances. As such, a conventional lens may provide limited use.
A bifocal lens was created to provide multiple focal lengths for the lens wearer or application where there is a need for varying visual acuity, for example, for reading and distance vision. However, this bifocal lens has fixed focal length regions, which also provides limited use.
In each of these examples, the lens is ground from a single material.